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Copyright (c) 2026 Hyojin Kim, Lærke Thorling, Rasmus Jakobsen
This work is licensed under a Creative Commons Attribution 4.0 International License.
Abstract
This data set provides a comprehensive assessment of groundwater partial pressure CO2 (pCO2) across Denmark, spanning more than three decades (1988–2024). Using groundwater chemistry data from the national borehole database, Jupiter, pCO2 levels were calculated and compared using two distinct approaches: (1) geochemical modelling via PHREEQC; and (2) simplified carbonate equilibria using only pH and alkalinity. While the latter is widely used for its simplicity, the PHREEQC method offers more accurate estimates by accounting for ionic strength and complexation. Despite Denmark’s extensive public archive of groundwater chemistry, pCO2 values have remained largely unavailable to the scientific community due to data complexity. This data set addresses this data gap through rigorous cleaning and the flagging of potentially contaminated samples to ensure high data fidelity. The resulting long-term, large-scale overview is essential for elucidating the role of groundwater in the carbon cycle and its spatiotemporal dynamics. Furthermore, these data establish critical baseline conditions necessary for monitoring and protecting groundwater resources in the context of the future CO2 injection and storage in deep geological reservoirs.
How to Cite
Share
Copyright (c) 2026 Hyojin Kim, Lærke Thorling, Rasmus Jakobsen
This work is licensed under a Creative Commons Attribution 4.0 International License.
Data Availability Statement
Three supplementary files are available, see link. These include the data "Groundwater_pCO2.xlsx", "Readme.txt" and Supplementary Figure S1 "Supplementary_Figure".
Supplementary Files
Funding
This work was funded by the Danish Research Reserve (Forsknings-reserven 2025).Downloads
An annual collection of articles submitted to GEUS Bulletin and published throughout 2026. Published online only. This issue is open for submissions until the end of 2026.
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References
- Abril, G., Bouillon, S., Darchambeau, F., Teodoru, C.R., Marwick, T.R., Tamooh, F., Ochieng Omengo, F., Geeraert, N., Deirmendjian, L., Polsenaere, P. & Borges, A.V. 2015: Technical note: large overestimation of p CO2 calculated from pH and alkalinity in acidic, organic-rich freshwaters. Biogeoscience 12(1), 67–78.
- Curtis Monger, H., Kraimer, R.A., Khresat, S., Cole, D.R., Wang, X. & Wang, J. 2015: Sequestration of inorganic carbon in soil and groundwater. Geology 43(5), 375–378.
- Dideriksen, K. 2025: [Code for] Parametric Study – PHREEQC. https://geusgitlab.geus.dk/geochemical-modelling/parametric-study-phreeqc/-/tree/53f86968d1b3b2f3975c4545cc909d07d5f9daa9/ (Accessed August 2026)
- Hansen, M. & Pjetursson, B. 2011: Free, online Danish shallow geological data. Geological Survey of Denmark and Greenland Bulletin 23, 53–56.
- Harned, H.S. & Davis, R. 1943: The ionization constant of carbonic acid in water and the solubility of carbon dioxide in water and aqueous salt solutions from 0 to 50°. Journal of the American Chemical Society 65(10), 2030–2037.
- Harned, H.S. & Scholes, S.R. 1941: The ionization constant of HCO 3 – from 0 to 50°. Journal of the American Chemical Society 63(6), 1706–1709.
- Miljø og Ligestillingsministeriet. 2025: Drikkevandsbekendtgørelsen. https://www.retsinformation.dk/eli/lta/2025/1272 [In Danish only]
- Ministeriet for Fødevarer, Landbrug og Fiskeri. 2019: Bekendtgørelse om kvalitetskrav til miljømålinger (BEK nr 523 af 01/05/2019). https://www.retsinformation.dk/eli/lta/2019/523 (Accessed August 2026)
- Morel, F., Hering, J.G. & Sigg, L. 1993: Principles and applications of aquatic chemistry. John Wiley & Sons Inc, New York.
- National Institute of Standards and Technology (NIST). 2025: NIST chemistry WebBook, SRD 69. https://webbook.nist.gov/chemistry/
- Parkhurst, D.L. & Appelo, C.A.J. 2013: Description of input and examples for PHREEQC version 3—A computer program for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations: U.S. Geological Survey Techniques and Methods, book 6, chap. A43, 497 p. U.S. Geological Survey, Denver. http://pubs.usgs.gov/tm/06/a43/
- Pötter, L., Tollrian, R., Wisotzky, F. & Weiss, L.C. 2021: Determining freshwater pCO2 based on geochemical calculation and modelling using PHREEQC. MethodsX 8, 101430.
- Raymond, P.A., Hartmann, J., Lauerwald, R., Sobek, S., McDonald, C., Hoover, M., Butman, D., Striegl, R., Mayorga, E., Humborg, C., Kortelainen, P., Dürr, H., Meybeck, M., Ciais, P. & Guth, P. 2013: Global carbon dioxide emissions from inland waters. Nature 503(7476), 355–359.
- Stumm, W. & Morgan, J.J. 1996: Aquatic chemistry: chemical equilibria and rates in natural waters, 3rd edition. Wiley, New York.
- Thorling, L. 2023: Groundwater sampling: technical guidelines.
- Thorling, L., Nyrop Albers, C., Hansen, B., Kidmose, J., Johnsen, A.R., Hilleke Mortensen, M., Troldborg, L. & Voutchkova, D. 2025: Grundvandsovervågning. Status og udvikling 1989–2024. www.geus.dk
